1 INVESTIGATING ABIOTI C FACTORS INFLUENCIN G THE ABUNDANCE OF FRANKLINIELLA BISPIN OSA IN BLUEBERRIES, AND THE DEVELOPMENT OF A PREDICTIVE RISK MODE L FOR THRIPS DAMAGE IN NORTH CENTRAL FLORIDA By TAMIKA A. GARRICK A THESIS PR ESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR TH E DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2013
2 2013 Tamika A. Garrick
3 To Koriean, K hamron, Kourtni and my wonderful family
4 ACKNOWLEDGMENTS I am grateful to God Almighty for without his countless blessings and grace, this thesis would not have been possible. I would like to express my deepest appreciation to my committee chair, Dr. Os car Liburd, for accepting me into his program and granting me the privilege to gain experience in IPM research. His helpful comments, probing questions and remarkably supportive attitude enabled my success. I would also like to thank Drs. Joe Funderburk an d Clyde Fraisse who served on my committee for their input and critical review of this manuscript. I also thank Drs. Daniel Wallach and Senthold Asseng for their insightful guidance and assistance with the development of my model. I thank the past and curr ent staff and students of the Small Fruit and Vegetable IPM laboratory for their assistance and guidance during my research. I would like to thank all the wonderful people in my life whose scientifi c, financial and moral support made this degree possible. I owe a huge debt of gratitude to so many and offer each of you my sincerest thanks. To my sister Nadine Garrick Grant and my parents who have always been supportive of my endeavors, I am greatly appreciative of all your efforts.
5 TABLE OF CONTENTS pag e ACKNOWLEDGMENTS ................................ ................................ ................................ .. 4 LIST OF TABLES ................................ ................................ ................................ ............ 7 LIST OF FIGURES ................................ ................................ ................................ .......... 8 ABSTRACT ................................ ................................ ................................ ................... 11 CHAPTER 1 INTRODUCTIO N ................................ ................................ ................................ .... 13 Blueberries ................................ ................................ ................................ .............. 13 Justification ................................ ................................ ................................ ............. 15 Specific Objectives ................................ ................................ ................................ 16 2 LIT ERATURE REVIEW ................................ ................................ .......................... 18 Flower Thrips ................................ ................................ ................................ .......... 18 Southern Highbush Varieties ................................ ................................ ............ 21 Rabbiteye Varieties ................................ ................................ .......................... 23 Diseases ................................ ................................ ................................ ........... 24 Arthropod Pests ................................ ................................ ................................ ...... 26 3 INFLUENCE OF VARIETAL PLANTING ON THE ABUNDANCE AND DISTRIBUTION OF FRANKLINIELLA BISPINOSA (THYSANOPTERA: THRIPIDAE) SMALL PLOTS OF RABBITEYE AND SOUTHERN HIGHBUSH BLUEBERRIES IN FLO RIDA ................................ ................................ .................. 31 Materials and Methods ................................ ................................ ............................ 32 Plot Layout and Location ................................ ................................ .................. 32 Monitoring ................................ ................................ ................................ ......... 33 Statistical Analysis ................................ ................................ ............................ 34 Results ................................ ................................ ................................ .................... 34 Discussion ................................ ................................ ................................ .............. 40 4 EFFECT OF H UMIDITY ON THE REPRODUCTIVE CAPACITY OF FRANKLINIELLA BISPINOSA AND FRANKLINIELLA OCCIDENTALIS (THYSANOPTERA: THRIPIDAE) ................................ ................................ ........... 51 Materials and Methods ................................ ................................ ............................ 53 Colony Establishment ................................ ................................ ....................... 53 Humidity Experiments ................................ ................................ ...................... 54 Results ................................ ................................ ................................ .................... 55
6 Discussion ................................ ................................ ................................ .............. 56 5 DEVELEOPMENT OF A RISK BASED PREDICTIVE MODEL FOR FRANKLINIELLA BISPINOSA IN SOUTHERN HIGHBUSH BLUEBERRIES GROWN IN FLORIDA ................................ ................................ ............................. 61 Materials and Methods ................................ ................................ ............................ 64 Model Development ................................ ................................ ......................... 64 Data Collection ................................ ................................ ................................ 65 Results ................................ ................................ ................................ .................... 65 Parameter Estimation ................................ ................................ ....................... 66 Validation ................................ ................................ ................................ .......... 66 Discussion ................................ ................................ ................................ .............. 66 6 LABORATORY REARING PROTOCOL FOR ESTABLISHMENT AND MAINTENANCE OF A COLONY FOR FRANKLINIELLA BISPINOSA (MORGAN) ................................ ................................ ................................ ............. 72 Materials and Methods ................................ ................................ ............................ 73 Results and Discussion ................................ ................................ ........................... 75 7 CONCLUSION ................................ ................................ ................................ ........ 79 LIST OF REFERENCES ................................ ................................ ............................... 81 BIOGRAPHICAL SKETCH ................................ ................................ ............................ 88
7 LIST OF TABLES Table page 5 1 Description of Forrester diagram of system of Frankliniella bispinosa in a blu eberry planting ................................ ................................ ............................... 70
8 LIST OF FIGURES Figure page 3 1 Mean number of adult thrips per flower sample recorded from each treatment per week on commercial farm in Citrus Co. in 2012. Error bars represent standard error of the mean ................................ ................................ ................. 42 3 2 Mean number of thrips per flowers sample recorded from each treatment per week and separ ated into adult and larval life stages. Data recorded from a commercial farm in Citrus Co. in 2012. Error bars represent the standard error of the mean ................................ ................................ ................................ 43 3 3 Mean number of thrips pe r sticky trap recorded from each treatment per week on commercial farm in 2012. Error bars represent standard error of the mean ................................ ................................ ................................ .................. 43 3 4 Average number of adult thrips per flower sample recorded from each treatment twice weekly on a commercial farm in 2013. Error bars represent standard error of the mean ................................ ................................ ................. 44 3 5 Mean number of thrips per flowers sample recorded from each treatment per week and separated into adult and larval life stages. Data recorded from a commercial farm in Citrus Co. in 2013. Error bars represent the standard error of the mean ................................ ................................ ................................ 44 3 6 Mean number of larval thrips per flower sample recorded from each treatment twice weekly on a commercial farm in 2013. Error bars represent standard error of the mean ................................ ................................ ................. 45 3 7 Mean number of adults thrips per flower sample recorded from each treatment collected twice weekly at PSREU in 2012. Error bars represent standard error of the mean ................................ ................................ ................. 45 3 8 Average num ber of adults thrips per flower sample recorded from each treatment collected twice weekly in rabbiteye blueberries at PSREU in 2013. Error bars represent standard error of the mean ................................ ................ 46 3 9 Total number of adults thrips per sticky trap recorded from each treatment collected once weekly in rabbiteye blueberries at PSREU in 2013. Error bars represent standard error of the mean ................................ ................................ 46 3 10 Total number of thrips sampled from flower buds in each treatment collected once per week at a commercial farm in Citrus Co. Florida in 2012. Error bars represent standard error of the mean ................................ ................................ 47
9 3 11 Total number of thrips caught on sticky traps in each treatment, collected once per week at a commercial farm in Citrus Co. Florida in 2012. Error bars represent standard error of the mean ................................ ................................ 47 3 12 Total number of thrips sampled from flower buds in each treatment collected twice per week at a commercial farm in Citrus Co. Florida in 2013. Error bars represent standard error of the mean ................................ ................................ 48 3 13 Total number of thrips caught on sticky traps in each treatment, collected once per week at a commercial farm in Citrus Co. Florida in 2013. Error bars represent standard error of the mean ................................ ................................ 48 3 14 Total number of thrips per flower sample recorded from each treatment collected twice weekly at PSREU in 2012. Error bars represent standard error of the mean ................................ ................................ ................................ 49 3 15 Total number of thrips caught on sticky traps in each treatment, collected once per week at PSREU in 2012. Error bars represent standard error of the mean ................................ ................................ ................................ .................. 49 3 16 Total number of thrips per flower sample recorded from each treatment collected twice per week at PSREU in 2013. Error bars represent standard error of the mean ................................ ................................ ................................ 50 3 17 Total number of thrips recorded per treatment on sticky traps collected once weekly in rabbiteye blueberries at PSREU in 2013. Error bars represent standard error of the mean. ................................ ................................ ................ 50 4 1 Mean reproductive capacity of F. bispinosa incubated at 23C and four different Relative humidities (80%, 70%, 55% and 40%). Error bars represent the standard error of the mean ................................ ................................ ........... 59 4 2 Mean reproductive capacity of F. occidentalis incubated at 23C and four different Relative humidities (80%, 70%, 55% and 40%). Error bars represent the standard error of the mean ................................ ................................ ........... 59 4 3 Mean time taken for F. bispinosa (FFT) and F. occidentalis (WFT) larvae to emerge following ovipositional period of adults at 23C and varying relative humidities (40%, 55%, 70% and 80%). Error bars represent the standard e rror of the mean. ................................ ................................ ............................... 60 5 1 Relational diagram describing the components of the system for Frankliniella bispinosa in SHB blueberries in Florida ................................ .............................. 68 5 2 Simulated population of T. imaginis overlaid on a plot of the average population observed for a 7 year period 1932 7 at the Waite Research Institute ................................ ................................ ................................ ............... 69
10 5 3 Simulated values using temperature data from Florida 2012 compared to recorded abundance of thrips in flower and sticky trap samples collected from the variety Star at a farm in Marion Co. Florida ................................ .......... 69 5 4 Simulated values using temperature data from Florida 2013 compared to recorded abundance of thrips in flower and sticky trap samples collected from the variety Star at a farm in Marion Co. Florida ................................ .......... 70 6 1 Illustration of layout of rearing containers for F. bispinosa with the lid removed ................................ ................................ ................................ ............. 77 6 2 Picture of rearing container (with lid at tached) prior to being placed in the environmental chamber ................................ ................................ ...................... 77 6 3 Average relative humidity of the interior of the environmental chamber for a 7 week period ................................ ................................ ................................ ........ 78
11 A bstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science INVESTIGATING ABIOTI C FACTORS INFLUENCIN G THE ABUNDANCE OF FRANKLINIELLA BISPIN OSA IN BLUEBERRIES, AND THE DEVELOPMENT OF A PREDICTIVE RISK MODE L FOR THRIPS DAMAGE IN NORTH CENTRAL FLORIDA By Tamika A. Garrick December 2013 Chair: Oscar E Liburd Major: Entomology and Nematology The usefulness of mixed cropping as a potential IPM management tool for the control of Florida flower thrips, Frankliniella bispinosa Morgan was investigated in southern highbush (SHB) (var. Emerald and Jewel) a nd rabbiteye (var. Powderblue and Brightwell) blueberries at two sites. At each site, a mixed plot of the two varieties was compared with single stands of each variety. The mixed plots were not effective at reducing flower thrips populations in both SHB an d rabbiteye varieties. Relative humidity has an effect on the time taken for larvae of F. bispinosa and western flower thrips, F. occidentalis Fitch to hatch. Frankliniella occidentalis generally emerged later than F. bispinosa and there is an increase in time with a decrease in relative humidity. Frankliniella bispinosa requires a higher humidity than F. occidentalis to reproduce; and has a higher reproductive capacity than F. occidentalis when compared in this study. The effectiveness of a temperature ba sed predictive model developed to forecast thrips abundance was tested on thrips population in SHB blueberries in 2012 and 2013. The output of the model was not always correlated with field observations; therefore,
12 model improvements to include RH and crop phenology are necessary before the model can be recommended. Establishment of a colony of F. bispinosa is necessary to increase our understanding of its biology and facilitate greater research. Establishment and maintenance of colonies require a constant temperature of 23C at 7510% RH. The overall study contributed to a better understanding of thrips ecology and management in southern blueberry production
13 CHAPTER 1 INTRODUCTION Blueberries In Florida, blueberries are a high value crop with a total valu e estimated to be 78 million dollars in 2011, cultivated on over 1,609 hectares (personal communication, Bill Braswell), however, there are millions of dollars lost yearly due to damage caused by thrips. Damage caused by thrips feeding on flower buds of bl ueberries can affect marketable yields. The use of reduced risk insecticides have been shown to only moderately reduce thrips populations and indiscriminate use of insecticides can lead to insecticide resistance, negative effects on non target organisms in cluding human and environmental degradation. North American blueberries belong to the family Ericaceae and the genus Vaccinium subgenus Cyanococcus Southern highbush [SHB] ( V. corymbosum L. x V. darrowi an interspecific hybrid) (Camp 1945) is the principa l species grown in Florida occupying more than 80% of the total acreage. Southern highbush varieties were developed from V. corymbosum L. introgressed with either V. darrowi Camp or another low chill southern blueberry species; this hybrid requires less ch ill hours to initiate reproductive development (Kalt et al. 2001, Lyrene and Sherman 2000)) and results in earlier fruit set and harvest giving an advantage in the early season fresh markets when prices are higher. This excellent market window from March t o early May has been the 2004). Alternatively, rabbiteye varieties ( V. virgatum Aiton) have been commercially available in Florida since 1890 when wild plants in North ern Florida were selected and
14 planted out. Rabbiteye blueberries are more vigorous and drought resistant than SHB. Berries have good flavor and large size (Austin 1979). Rabbiteye occupy less than 20% of the planting in Florida. Southern Highbush is grown commercially in Florida primarily from Arcadia in the south central part of the state to Jacksonville in the north central region. Standard production practices for SHB involve the use of Dormex (hydrogen cyanide) for freeze protection and pruning to stim ulate early and growth for the next season (Williamson 1999, 2000, 2001, 2006). Blueberry bushes are pruned immediately after harvest to promote vigorous growth. Protection of the crop from freezes is important as it mitigates the effects of thrips on the crop. The healthier the crop is, the better it is able to withstand damage from thrips (Williamson et al. 2012 b Williamson 2000). Blueberries that ripen in April come from flowers that are pollinated in February. Blueberry flowers become vulnerable to fr eezes weeks before they are pollinated and can be killed by late freezes that occur in late January or early February. Thus, blueberry flowers that are not protected are oftentimes killed, which leads to a reduction in yield. The use of overhead irrigation is the most common method used in Florida against freeze damage to protect the blueberry crop. In some north central counties, late freezes between February 20 and March 20 have been responsible for the loss of some of the crop even when protected by ove rhead irrigation. The protection provided to the crop by overhead irrigation is lost if the temperature drops below 3C accompanied by wind speeds above 24 km/h (Williamson et al. 2012 b Williamson 2000). When the wind is calm (< 5 km/h) wind
15 machines and helicopters can be used to raise the temperature by about 4C. However, on nights with a mild to strong wind, helicopters and wind machines are not able to warm the air sufficiently to provide freeze protection and for this reason it is seldom used (Willi amson et al. 2012 b ). In addition to freeze protection, other factors including diseases, arthropods, environmental conditions and varietal differences could significantly affect production. Justification The rearing of Frankliniella bispinosa (Morgan) has been done by a number of researchers over the years; however, no established rearing protocol is available. Being such a significant problem in blueberry production in Florida, it is necessary to have established guidelines by which a colony of F. bispinos a can be successfully reared in order to enable progress into research of this pest. Mixed cropping is an Integrated pest management (IPM) technique that has been successful in controlling a number of insect pests in agricultural systems. The need to inves tigate IPM tools that are not currently included in the IPM program for blueberries grown in Florida has increased with rising public demand for reductions in pesticide use, the increasing occurrence of pesticide resistance and the growing need to improve efficiency of farm operations and reduce inputs. Growers already utilize mixed cropping as a means to improve pollination and to extend the harvest of their berries. It would be useful to evaluate if this current practice of mixed cropping has an added ben efit of managing thrips populations. The use of models to forecast diseases or to predict pest occurrence is a relatively new trend in agriculture that seeks to remove much of the guesswork that had previously been involved in crop protection. Research in integrated pest management
16 (IPM) has led to a bank of knowledge, which now requires computer aided methods for their integration, interpretation and delivery (Coulson 1992). The use of reduced risk insecticides have been shown to only moderately reduce th rips populations and indiscriminate use can lead to insecticide resistance enhanced by the cryptic nature of the flower thrips. Frankliniella bispinosa population development is highly influenced by environmental factors including temperature and humidity. In New Jersey where the eastern flower thrips ( Frankliniella tritici Fitch) is common, a degree day model to predict their abundance has been developed and is currently being used in blueberry growing areas in the northern United States; this model is use less in Florida because of the differences in temperature, pest species and the inflexibility of a model derived by regression analysis. Prediction of thrips development based on weather models can be a very useful tool in pest management. The development of a predictive model that is user friendly and available to blueberry growers would be very useful as a decision making tool to aid in the management of the Florida flower thrips. Specific Objectives My goal was to target the key pest, Frankliniella bisp inosa (Morgan) and study its environmental conditions including temperature to develop a model for predicting thrips abundance and potential damage in the field. Furthermore, I studied the design of blueberry plantings (field layout) to develop management programs for F. bispinosa The specific objectives of this study were to 1) study blueberry plantings; pure stand versus mixed plantings to determine if thrips populations is lower in one type of planting (pure or mixed) or the other. 2) investigate the ef fects of humidity on the reproductive capacity of F. bispinosa and F. occidentalis. 3) develop a model to predict the potential
17 risk posed to blueberry crops by F. bispinosa and 4) develop an improved rearing protocol for F. bispinosa
18 CHAPTER 2 LITERATU RE REVIEW Flower Thrips Thrips belong to the order Thysanoptera and are minute, slender insects with fringed wings. They are distributed worldwide but are most common in tropical and sub tropical regions. Most thrips feed by using their mouthparts to pierc e and suck fluid from plant parts, a few feed on fungi, some are predatory and other feed on mosses and detritus (Lewis 1997 a ). The members of this order only possess one developed mandible which is on the left side; the mandible on the right side is re ab sorbed during embryogenesis. Most of the members of the Thysanoptera have two pairs of wings with marginal fringes of cilia giving it a fringed appearance, however, some members are apterygous either lacking wings as adults or losing them sometime during t heir adult life (Mound 2005). There are a number of thrips species that affect blueberries in North America. Most of the species that are pests of blueberries belong to the family Thripidae and the subfamily Thripinae. In Florida, Frankliniella bispinosa ( Morgan) is the main thrips species that affects blueberries. Thrips feed on floral parts of the plant leading to a reduction in the quality and quantity of the fruits produced. Fruit damage can also be as a result of adult oviposition within flower tissues with the larvae burrowing out upon emergence (Liburd et al. 2009 b England et al. 2007). Frankliniella bispinosa (Morgan), the Florida flower thrips, is the most important early season pest of SHB in Florida Females lay their eggs inside the ovaries and as the larvae emerge they leave scars behind on the developing fruit, which significantly affects the aesthetics of these fruits, thus reducing marketability and yields. Frankliniella
19 bispinosa can be distinguished from the other major thrips species ( F. o ccidentalis Pergande and F. tritici Fitch) in Florida by slide mounting specimen and examining the base of the antenna where the first antennomere is swollen and the edges are more or less sharp. There is also two well developed and sclerotized setae in th e second antennal segment (Arevalo et al. 2009 b ). The control of thrips using traditional measures has been shown to be a challenge. The use of commercially available predators: Thripor I ( Orius insidiosus ), Thripex plus ( Amblyseius cucumeris ) and a combin ation of both as biological control agents has been shown to be an ineffective control measure due to the short period during which flower thrips are present in the field (Arevalo et al. 2009 b ). Biocontrol agents need prey to be present over an extended ti me to build up effective predator populations. Earlier, Childers and Bullock (1999) evaluated the effect of controlling adult F. bispinosa on the fruit set of Navel and Valencia oranges or Marsh grapefruit varieties by controlling F. bispinosa on the flowe rs during bloom. They used an insecticide and concluded that it was more important to prevent establishment of larval thrips populations in the field than to control their populations. ages of development in blueberry plantings (Arevalo and Liburd 2007). The dispersal behavior of flower thrips was investigated in blueberry ( Vaccinium spp. ) fields in Florida and which are large numbers of thrips aggregated in a small area started to form about 5 7 days after bloom. The highest concentration of thrips was found to be inside the canopy of the
20 blueberry bushes. These hot spots were determined to form randomly (Areva lo and Liburd 2007). Thrips appear to immigrate into blueberry plantings from adjacent hosts. Rhodes and Liburd (2011) investigated flower thrips dispersal from alternate hosts into SHB and found several reproductive hosts of F. bispinosa including: Carol ina geranium ( Geranium carolinianum L.), white clover ( Trifolium repens L.), and wild radish ( Raphanus raphanistum L.). However it was shown that clover was not a significant source of inoculum for thrips into blueberry fields although they are found abund antly adjacent to the fields. Earlier, Lewis (1997 b ) reviewed the literature on flight and dispersal of thrips and reported that there were intense periods of flight associated with each species. Several factors including temperature, wind speed and host a vailability appear to influence dispersal. Biology Life cycle: Frankliniella bispinosa has 6 life stages: egg, 1 st larval instar, 2 nd larval instar, propupa, pupa and adult (Triplehorn et al. 2005). The propupa and pupa are soil or debris borne while the other stages are found in flowers and buds (Childers et al. 1999). Thrips have a very short life cycle of approximately 18 22 days depending on environmental conditions with several generations per year (Liburd et al. 2009). Injury Frankliniella bispinosa adults and larvae are known to feed on floral parts such as the ovary, style, anthers and petals of buds and flowers (Arevalo 2006). Injury to the ovary during fruit set results in dehydration to the fruit and increase in failure of fruit set, which resul ts in reduced yields (Arevalo 2006). Punctures were about 2.5 5 m in diameter and from 12 84 m in depth oftentimes spanning as many as five layers
21 of cells. Feeding results in cellular evacuation, necrosis, plasmolysis and collapse of affected tissues Oviposition and eclosion have been reported from pistil, calyx, petals and filaments which can affect the quality of fruits (Childers 1991). Management The control of thrips in blueberry has shifted from the exclusive use of conventional pesticides to a more integrated management approach where compatible IPM strategies are used. In a study to compare reduced risk and conventional insecticides for controlling thrips, six insecticides were compared to the grower standard malathion.Treatments included acet amiprid (Assail 70W ), novaluron (Diamond ), Spinosad (SpinTor), thiamethoxam (Actara) and acetamiprid (Assail a different formulation). Three reduced risk insecticides including acetamiprid, novaluron and thiomethoxam were shown to significantly reduce t he thrips ( F. bispinosa ) population when compared with malathion (Liburd et al. 2010). The reduced risk insecticide Spintoram under the trade name Delegate is now the standard product used to suppress thrips numbers in blueberry plantings. Delegate works well in a thrips IPM program because it conserves natural enemies. It is best to spray Delegate in the morning or late in the evening because it has a minimal effect on bees when dried; bees are less active during these times of the day and so it would no t affect them adversely (England et al. 2007). Another reduced risk insecticide registered for thrips control is Acetamiprid (Assail). Southern Highbush Varieties The principal varieties of SHB grown in Florida are: Star, Emerald, Jewel, Millenia and Winds or. Blueberry varieties are usually grown in mixed stands (several varieties) to encourage pollination or in pure stand where only one variety is grown in a small block.
22 Star. This cultivar was released commercially in 1996 because of its good fruit qualit ies, low chill requirement, high vigor, concentrated early ripening, ease of harvesting and manageability in the packing houses. Although it is considered a low yielding variety, Star is planted from Ocala, FL in the South to North Carolina on mixed holdin gs where cross pollination enhances productivity. This variety is preferred because of its short bloom to ripe interval of about 3 weeks. Star also offers medium to high resistance to a number of key diseases such as root rot, stem canker and stem blight; however, leaf spotting fungal diseases are common in Star (Lyrene and Sherman 2000, Arevalo Rodriquez 2006). Emerald. This variety has been commercially available since 2001 and is well adapted to north central Florida and is rarely ever grown south of Oca la, FL. It is also grown in parts of Georgia and California (U.S.A), Argentina, Chile, Australia and Spain (Lyrene 2008; personal communication, Olmstead). Emerald is a high yielding variety and is resistant to stem canker. It shows moderate to high resist ance to common leaf diseases in Florida but is very susceptible to systemic infections of stem blight and phytophthora root rot (Lyrene 2008, Lyrene 2001). In a study conducted on four varieties of SHB, Emerald tolerated the highest thrips population witho ut suffering increased injury to the fruits (Rhodes et al. 2012). Jewel. This variety has a moderately low chilling requirement with a consistent early ripening of the berries with the first commercial harvest around April 15 (Lyrene 2001). It was released by the University of Florida as a variety that produces large fruits. Jewel has a tart to sweet flavor and good texture (Williamson et al. 2004, Lyrene 2001). It is however, necessary to leave the fruits on the bushes for extended periods to allow
23 accumul ation of sugars to reduce the tart flavor (Arevalo 2006). Jewel is commonly grown in north and central Florida and is considered to be moderately resistant to cane canker ( Botryosphaeria corticis ) stem blight ( Botryosphaeria dothidia ) but moderately susce ptible to root rot ( Phythophthora cinnamomi ) (Arevalo 2006, Lyrene 2001, Williamson et al. 2004). Millennia. This variety was released commercially in 2001 by the University of Florida as a variety that produces large firm berries. It is light blue in colo r and has a great picking scar. Millenia usually has a mild and pleasant flavor; however, the taste can be bland on poorly leafed or overcrowded plants (Lyrene 2002 a Williamson et al. 2004). It has high resistance to cane canker, medium resistance to phyt ophthora root rot, low to medium resistance to stem blight but is highly susceptible to the fungus botrytis (Arevalo 2006, Lyrene 2002 a ). Windsor. This variety produces a vigorous bush with a slightly spreading growth habit. The berries are large averagin g around 2.4 grams and are firm and dark blue in color with a sweet, pleasant flavor (Lyrene 2002 b ). If the weather gets too hot or the fruits are not picked on time, fruit scars develop; this complicate packing and reduces the post harvest quality and she lf life and has resulted in this variety losing favor among growers (Williamson et al. 2004, Arevalo 2006). Rabbiteye Varieties The two most common varieties of Rabbiteye blueberries grown in Florida are: Powderblue and Brightwell.
24 Powderblue. This is a m ore recent variety that has almost completely displaced good qualities in areas where Tifblue had failed. The bush is upright and vigorous and very productive and is co nsidered a very reliable variety in northern Florida. Powderblue is resistant to cracking unlike its predecessor Tifblue. Self pollination is rather uncommon in Rabbiteye but Powderblue is unique in that it is able to fruit well when self pollinated (Willi amson et al. 2004). Brightwell. This was released by the University of Georgia in 1983 as a commercial variety because it combines the high and dependable yield with the high quality of the berries it produced. The fruits are medium sized and have a dry sc ar; it has a good flavor and can be mechanically harvested. Disease resistance is one of its most admirable qualities (Williamson et al. 2004, Lyrene 2002 c ). Diseases Several important diseases affect both rabbiteye blueberry and SHB production. These in clude: phytophthora root rot, blueberry stem blight, botrytis flower blight and bacterial leaf scorch. Phytophthora root rot disease is caused by the fungus, Phytophthora cinnamoni Rands. It usually occurs where drainage is poor or marginal and is favored by high temperatures (Williamson et al. 2012). On blueberries, root rot is initially indicated by a loss of plant vigor and a subsequent yellowing or premature reddening of the leaves with defoliation of green stems. Infected transplants, contaminated pot s, soil or irrigation water can serve as inoculum for infections within a field (Cline et al. 2006).
25 Infected plants typically have a poor root system reducing anchorage and water uptake; these plants are the first to wilt on dry days and will die over ext ended periods of water stress (Cline et al. 2006, Williamson et al. 2012). Control of root rot in blueberries can be achieved by increasing drainage in the field, avoid over irrigating, ensure that clean transplants are planted, avoid planting in a known i nfested area and to use treated irrigation water where possible (Cline et al. 2006, Williamson et al. 2012). Blueberry stem blight C an be caused by Botryosphaeria species, Neofuscicoccum ribis or Lasiodiploda theobromae Botryosphaeria ribis and Botryosph aeria rhodina have been identified as the primary fungi associated with stem blight. Botryosphaeria dothidea is believed to play a minor role in causing blueberry stem blight. This disease leads to necrotic branches with attached leaves; the vascular regio n of the affected branches will turn brown leading to premature death of the affected plants (Wright et al. 2009 a 2009 b 2009 c ). Blueberry stem blight is more common in SHB than in rabbiteye varieties where some varieties are extremely susceptible (Willia mson et al. 2012 a ) and is considered the most important disease affecting the blueberry industry (Wright et al. 2009 c ). Plant stress such as over fruiting, poor leafing, nutrient and water deficiencies can increase the susceptibility to stem blight. No che mical means of control are available for this disease; the best management program entails good cultural practices (Williamson et al. 2012 a ). Botrytis flower blight C aused by the fungus Botrytis cinerea, affects wounded or senescent petals of both rabbite ye and SHB varieties but is more severe in rabbiteye varieties. The petals usually fall from the flower after pollination before senescing; however, frost damage may facilitate infection by this fungus of the
26 damaged floral parts (Harmon 2011, Williamson e t al. 2012 a ). The disease spread is aided by relatively high humidity and can lead to yield reduction. In severe cases berries may be malformed or develop a rot if favorable disease conditions arise. High humidity caused by overhead irrigation for frost pr otection during flowering increases the likelihood of developing this disease. Botrytis blossom blight can be managed primarily through fungicide applications and by minimizing the period over which leaves and floral parts remain wet (Harmon 2011). Bacteri al leaf scorch I s a disease of blueberries caused by the bacterium, Xylella fastidiosa. This disease is relatively new and was only first reported in Florida in 2009. It is an emerging disease that threatens the SHB industry especially the variety where the potential yield loss is great (Harmon 2009). Xylella fastidiosa is a xylem limited disease and affects the plant by blocking the xylem tubes thus preventing the movement of materials up the plant. The disease is first manifested as a leaf scorch then after leaf drop, the stem and twigs will appear yellow in color; plants will eventually die. To date, cultural practices are the best management options since chemical control will not kill the bacterium, and are best used to control the leafhopper ve ctors (Brannen et al. 2011). Arthropod Pests Arthropod pests of blueberries in Florida are in three categories early, mid and late season. Key early season pests Blueberry gall midge (BGM) Dasineura oxycoccana (Johnson) was first observed damaging flowe r buds in blueberry plantings in Florida in 1992 (Lyrene et al.
27 1992); it had previously been known to affect vegetative stems in blueberries and cranberries in states north of Florida (Lyrene et al. 1992). Recently, BGM was determined to be a cryptic spec ies of the cranberry tipworm from which it is morphologically indistinguishable (Mather et. al. 2012). Heavy infestation of gall midge in blueberry plantings can lead to reduced productivity with low fruit set (Liburd et al. 2010). Symptoms of BGM infestat ion include curled leaves, premature floral bud abortion, stunted growth and blackened leaf tips; many of these symptoms can easily be mistaken for frost damage. These symptoms can be more severe after mild winters in more southern locations. Both SHB and rabbiteye varieties are susceptible; however, up to 80% of rabbiteye plantings can be destroyed if infestation is not treated (Liburd et al. 2010, Lyrene et al. 1992, Steck et al. 2011). Gall midges are dipterans and belong to the family Cecidomyiidae; the adult female lays eggs in the mid to inner bud scales, these eggs will hatch into larvae, which will feed on the developing buds the larva is harder to manage with insecticide treatments because of their cryptic habit. Adults are easily killed with insect icides (Liburd et al. 2010, Steck et al. 2011). Blueberry bud mite. Acalitus vaccinii (Keifer) is an eriophyid mite, which is a known pest of Vaccinium under the large outer bud scales with a few under the short basal bud scales and were rarely ever found deeper within the bud. In early spring as the buds develop, the mites will migrate within the bud to live among the developing clusters; this will result in the formation of galls or hypertrophy of the damaged parts (Fulton 1940).
28 Bud mites require a minimum of 15 days to complete their life cycle at 19 C. They reach their maximum population in early spring and are rarely found during the summer with the population rebounding in the fall. Mite fe eding during the spring will result in the reddening and swelling of the base of the bud scale, which will appear rosetted and may desiccate or fail to open. Berries and flowers from infested buds usually have small blister or pimples, which makes the crop unmarketable. Symptoms will appear roughly 14 days after infestation. It has been estimated that bud mites can lead to over 60% reduction in yield in blueberries although the full extent of the damage caused by this pest is still unknown (Baker et al. 197 0, Fulton 1940, Weibelzahl and Liburd 2010). Some cultivars are known to be more susceptible than others but to date none has shown complete resistance to this pest; cultural practices such as pruning incorporated into a good management program is the best way to manage this pest. It has been shown that the use of reduced risk pesticides such as abamectin and horticultural oils could be effective in a bud mite management program (Weibelzahl and Liburd 2010). Mid season pests in Florida The key mid season p ests in Florida include spotted wing drosophila and cranberry fruitworm. Spotted wing drosophila (SWD). Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) is an emerging pest in SHB. It was first detected in Florida in Hillsborough County in 2009. Dur ing 2012, SWD was found in 10 of the 14 farms sampled that encompassed all 8 counties in 2012 (Iglesias and Liburd 2012, unpublished data).
29 Female oviposits its eggs just below the skin surface of the fruit. Unlike most vinegar flies that generally prefer damaged or decaying fruit, the female SWD has a serrated ovipositor at the base of the abdomen that allows her to lay eggs in healthy, ripening fruits. Injury from SWD causes depressed scars on the fruit upon insertion of the ovipositor and browning and so ftening of the fruit from larval development, rendering fruit unmarketable and resulting in crop loss. Spotted wing drosophila has the potential to spread rapidly due to its short generation time. Recent laboratory observations show development time from 1 2 to 15 days at 65 C and up to 10 generations a year under California conditions (Walsh et al. in press). Cranberry fruitworm Acrobasis vaccinii Riley (Lepidoptera: Pyralidae) is common throughout the Eastern United States and Canada (Meyer & Cline 1997 ). The adult lays eggs in an aggregated manner on green berries primarily within the calyx; larvae hatch in 4 5 days and enter the berry (Mallampalli et al. 2002, Hutchinson 1954). Having entered the berry, the cranberry fruitworm will feed on up to 8 berr ies in a cluster to complete it 5 larval stages (Turner & Liburd 2007, Godin et al. 2002). As the larvae feed, it produces a web that often ties the berries it feeds on together (Turner & Liburd 2007, Hutchinson 1954). The larvae leaves frass within the be rries as it feeds which often spills out and clings to the webs, this makes the fruits unmarketable. Mature larvae will drop to the ground, where they will overwinter; pupation and emergence will occur the following spring (Turner & Liburd 2007). Late seas on or post harvest pests in Florida The main late season or post harvest pest on blueberries is the Blueberry leaf beetle.
30 Blueberry leaf (flea) beetle Colaspis pseudofavosa (Riley) is the main post harvest pest found within blueberry plantings in Florid a. In a survey conducted in the summer of 2008 in SHB, 68% of the beetles sampled were C. pseudofavosa whereas 32% were Systena frontalis (Fabricius) (Nyoike and Liburd unpublished data). The blueberry leaf beetle feeds on the foliage by biting and removi ng portion of the leaf; and prefers new, young leaves as opposed to older leaves that were a part of the spring flush. Previous studies showed that Mustang, Malathion and Imidan were the best insecticides that could be used to manage blueberry leaf beetles (Nyoike and Liburd unpublished data).
31 CHAPTER 3 INFLUENCE OF VARIETAL PLANTING ON THE ABUNDANCE AND DISTRIBUTION OF FRANKLINIELLA BISPINOSA (THYSANOPTERA: THRIPIDAE) SMALL PLOTS OF RABBITEYE AND SOUTHERN HIGHBUSH BLUEBERRIES IN FLORIDA The blueberry ind ustry in Florida is a relatively new one and some of the diseases and pests have not been fully investigated. Frankliniella bispinosa (Morgan) is an early season pest that feed on floral parts causing yield losses. The selection of a blueberry variety i n Florida depends on the location of the planting (northern Florida versus south central Florida) and the intended market of the grower. The most common southern highbush (SHB) blueberry varieties grown in Florida are Jewel, Emerald, Millenia, Star and Win central Florida but are restricted from being cultivated in the north and northwestern parts of the state due to late freezes that often damage the se early ripening varieties (Williams & Lyrene 2004). Rabbiteye varieties are later ripening and are grown in the northern parts of the state primarily for the u pick industry and for other local markets (Williams & Lyrene 2004). Rabbiteye varieties were the first commercial blueberries grown in Florida but have since been replaced by SHB and now accounts for less than 20% of the total blueberry acreage in Florida (personal communication Oscar Liburd). Blueberry varieties are usually grown in mixed stands to encourage pollination of flowers and subsequently increase marketable yields. In a few cases blueberry varieties are grown in pure stands where only one variety is grown in a small block. The use of mixed plots is an IPM cultural tactic that can be use d to reduce the abundance of some pests (Nyoike and Liburd 2010). Intercropping and mixed cropping are also practices
32 that have been proven to reduce pest numbers in vegetable and fruit crops (Liburd et al. 2008). The use of mixed plots to control disease s is well established in crops such as rice where rice blast disease incidence was lower in mixed plots than in pure stands of rice varieties (Genzhang 1989). The Onion thrips ( Thrips tabaci Lindeman) was controlled in a leek crop that was intercropped wit h clover and resulted in an improved quality of the harvest (Theunissen and Schelling 1996). The use of mixed cropping to suppress pest population has been widely studied using two or more species of study plants and has been shown to be effective at pest control (Matteson 1982, Liburd et al. 2008, Theunissen and Schelling 1996, Hooks et al. 1998) However, the possibility of using different cultivars of the same species in a mixed plotting system to control pests has not been widely explored. I hypothesized that having mixed plots of blueberry varieties (with different flowering dates) will sustain a lower population of flower thrips as opposed to a pure stand with a single variety. Therefore, the primary goal of this research was to investigate the effect o f planting mixed blueberry varieties on the population of flower thrips and as a possible tool to be used in flower thrips control in blueberries in Florida. Materials and Methods Plot Layout and Location The experiment was located in two blueberry planti ngs in North central Florida. Site 1 was a SHB commercial farm in Citrus County and site 2 was a Rabbiteye blueberry planting located at the University of Florida, Plant Science Research and Education Unit (PSREU) in Marion County. A randomized complete bl ock design with 3 treatments was used to test the effects of varietal planting on the distribution and
33 abundance of F. bispinosa On the commercial farm treatments 1 and 2 consisted of a single variety of SHB (Emerald or Jewel) and treatment 3 was a mixed planting of these two blueberry varieties (Emerald and Jewel). In the Rabbiteye planting at the PSREU, Treatments 1 and 2 were single variety of Rabbiteye blueberry (Powderblue or Brightwell) and treatment 3 was a mixed planting of these two varieties (Pow derblue and Brightwell). At the commercial farm each plot was 49 m 2 with 3 replicates per treatment and a total study area of 2078 m 2 In Marion Co. each plot was 5m 2 with 4 replicates per treatment. Monitoring Thrips population was monitored weekly usi ng white sticky traps (Great Lakes IPM Inc, Vestaburg, MI) and by inspecting flower clusters. Sticky traps One white sticky trap (15.2 x 20.3 cm) was hung in each plot within the canopy of the blueberry bush. Traps in the SHB were replaced weekly in 201 2 but twice weekly in 2013. The increased frequency to service traps in 2013 was due to making it easier to count thrips caught on the traps. Southern highbush and Rabbiteye blueberries flower for a short period (~3 4 wks) during the production season, the refore, flower and trap samples were collected for 3 weeks in both years of the study. Traps in Rabbiteye were left in the field for 72 hours and replaced once per week for the study period of 3 weeks in 2012 and 4 weeks in 2013. The difference in duration was due to the earlier start of the monitoring period in year 2 in SHB and an extended flowering period in rabbiteye blueberries in year 2. Traps were collected and taken to the Small Fruit and Vegetable IPM laboratory (SFVIPM) at the University of Florid a Entomology and Nematology department to be enumerated. The number of thrips caught was counted under a stereo microscope using a transparent grid overlaid on a cling wrap
34 urd et al. 2009). Flower samples Approximately 5 flower clusters (with about 5 opened flowers per cluster) were collected in a random manner from each plot on a weekly basis into 50 ml plastic vials (Fisher Scientific, Pittsburg, PA) containing approximat ely 30 ml of 70% ethanol. Samples were collected for 3 weeks for both years of study on the commercial farm of SHB in Citrus Co. At the PSREU, samples were collected for 4 weeks in 2012 and 6 weeks in 2013Samples were taken to the SFVIPM laboratory at the University of thrips were extracted from the floral parts and their numbers counted under a stereo microscope (10 X). The number of adult and larval thrips collected from flower and trap counts were recorded. Statistical Analysis Thrips data from traps and flowers were subjected to repeated measures analysis of variance using SAS 9.23 (SAS Institute Inc. 2012) to examine the effects of variety on thrips numbers and any po ssible interaction between variety and abundance throughout the monitoring period. One way ANOVA and means separation using Least Significant Difference (LSD) test (SAS Institute Inc. 2012) was done on individual dates to determine differences between trea tments (SAS Institute Inc. 2012). Results Population dynamics of thrips in SHB planting 2012. Flowers At the time when the first sample was taken flower thrips population was already high in all three cultivars exceeding 80 thrips per flower. The number o f adult thrips in each treatment was significantly different for 1 st and final sampling dates ( F = 9.99; df = 2, 24; P =
35 0.0007) and showed a general decline over the study period as shown in Fig 3 1. The interaction between thrips numbers and variety was not significant ( F = 0.23; df = 4, 8; P = 0.91); neither was the interaction between adult thrips numbers and block ( F = 0.51; df = 4, 8; P = 0.73). Analysis of the larval thrips counts for the period showed that February 15 th was significantly higher tha n the other two sampling dates ( F = 8.94; df = 2, 24; P = 0.0013). The interaction between larval thrips numbers and block was not significant ( F = 0.69; df = 4, 8; P = 062) and neither was the interaction between larval thrips numbers and variety ( F = 0.8 3; df = 4, 8; P = 0.54). When adult and larval data is summarized over the 3 week sampling period, it can be seen [Fig. 3 2] that adult thrips numbers were higher in Emerald for the two last sampling dates (weeks 2 &3) than Jewel. Traps The adult thrips population was significantly different between sampling dates ( F = 868.69; df = 3; P = 0.0012) [Fig. 3 3]. Thrips population analyzed by LSD was shown to be significantly higher on Feb 23 rd compared with Mar 3 rd but was comparable to numbers sampled on Fe b 10 th and Feb 15 th (F = 2.00; df = 3, 32; P = 0.13). The effect of the adult thrips and block interaction was not significant ( F = 0.8; df = 6, 12; P = 0.56). Similarly, the effect of the adult thrips and variety interaction was not significant ( F = 0.89; df = 6, 12; P = 0.53). Larval thrips population between the sampling dates were different with Feb 10 th being significantly lower than Feb 23 rd and Mar 3 rd ( F = 3.18; df = 3, 32; P = 0.05). There was no block effect ( F = 2.25; df = 2, 4; P = 0.22) or vari etal effect ( F = 0.52; df = 2, 4; P = 0.63). No interaction effects between larval thrips numbers and the blocks present ( F =
36 2.84; df = 6, 12; P = 0.058); neither was there an effect of an interaction between larval thrips numbers and variety ( F = 0.51; d f = 6, 12; P = 0.76). Population dynamics of thrips in SHB planting 2013. Flowers Adult thrips numbers were significantly different over the sampling dates ( F = 21.51; df = 4, 40; P = <0.0001) [Fig. 3 4]; population was significantly higher on Feb 4 th tha n on the other sampling dates. There was no effect of the interaction between adult thrips numbers and experimental block ( F = 1.91; df = 8, 16; P = 0.13) and no effect of the interaction between thrips numbers and varieties ( F = 2.17; df = 8, 16; P = 0.09 ). Larval thrips numbers (Fig. 3 6) were significantly higher on Feb 7 th than the other sampling dates ( F = 7.46; df = 4, 40; P = 0.0001); there was no difference between the sampling dates Feb 11 th 4 th and Jan 13st. The number of thrips in the mixed plo t (Jewel and Emerald) and the Jewel plots were 45 and 24, respectively on February 4 th On February 7 th the numbers in these same plots were 113 and 75. There was no block effect ( F = 1.31; df = 2, 4; P = 0.37) and no variety effect ( F = 0.54; df = 2, 4; P = 0.62). Traps The adult thrips population was significantly different over the sampling dates ( F = 3.49; df = 4, 40; P < 0.015). The number of adults in Emerald was significantly higher than Jewel on Feb 4 th 7 th and 11 th The effect of an interaction between block and thrips number was significant ( F = 3.65; df = 8, 19; P = 0.01). The effect of the interaction between adult thrips numbers and variety was not significant ( F = 1.71; df = 8, 16; P = 0.17). No block effect ( F = 4.72; df = 2, 4; P = 0.09) o r varietal effect ( F = 3.62; df = 2, 4; P = 0.13) was observed. Larval thrips numbers were significantly different over the study period ( F = 3.40; df = 4, 40; P = 0.017). The
37 th The effect of the interaction between larval thrips numbers and block was not significant ( F = 1.17; df = 8, 16; P = 0.37); the effect of the interaction between thrips numbers and variety was n ot significant ( F = 1.32; df = 8, 16; P = 0.30). Population dynamics of thrips in rabbiteye blueberry planting 2012. Flowers Adult thrips numbers (Fig. 3 7.) were significantly different over the course of the study ( F = 22.20; df = 6, 36; P < 0.0001) wi th a general decline over time. The effects of interactions between block and adult thrips numbers ( F = 1.66; df = 18, 36; P = 0.09) and variety ( F = 1.69; df = 12, 36; P = 0.11) were not significant. Larval thrips numbers for the same period was significa ntly different ( F = 11.12; df = 6, 36; P < 0.0001). No block effects were detected ( F = 1.59; df = 3, 6; P = 0.29) or varietal effects ( F = 0.41; df = 2, 6; P = 0.68). Traps. The number of thrips adults was significantly different between sample dates ( F = 10.20; df = 2, 12; P = 0.0026). The number of adult thrips sampled on April 13 th was lower when compared to April 6 th and 20 th ( F = 8.48; df = 3, 33; P = 0.001). No varietal effects ( F = 2.38; df = 2, 6; P = 0.17) or block effects ( F = 1.52; df = 3, 6; P = 0.30) were detected. Larval thrips sampled were significantly different ( F = 8.48; df = 2, 33; P = 0.0001) over the course of the study with the highest numbers recorded on Apr 6 th There was no effect of block ( F = 0.78; df = 3, 6; P = 0.55) or variety ( F = 5.53; df = 2, 6; P = 0.04) on this study. Population dynamics of thrips in rabbiteye blueberry planting 2013. Flowers The adult thrips numbers (Fig. 3 8.) were significantly different ( F = 26.14; df = 11, 66; P <
38 0.0001); however, there were no bloc k effects ( F = 1.26; df = 3, 6; P =0.40) and no varietal effects ( F = 0.75; df = 2, 6; P = 0.51). The number of adults collected on April 9 th was higher than all other sampling dates ( F = 22.56; df = 10, 121; P < 0.0001). Larval thrips numbers were also sig nificant for the duration of the study ( F = 8.34; df = 11; P < 0.0001). The number of larvae on Apr 5 th 9 th and 16 th were significantly higher than all other sampled dates ( F = 6.10; df =10, 121; P <0.0001). On April 5 th the number of larvae was higher in Powderblue than the other two treatments; on April 9 th Powderblue was higher than Brightwell but not the mixed plot. There was no block effect ( F = 2.10; df = 3, 6; P = 0.20) and no varietal effect ( F = 1.53; df = 2, 6; P = 0.29) detected. Traps Adult th rips population over the season was similar for the first 3 weeks of monitoring ( F = 40.08; df = 2, 33; P <0.0001). However, on the fourth sampling date, the number of adults caught in the variety Powderblue was higher than in Brightwell but not the mixed plot of both Powderblue and Brightwell (Fig. 3 9.). Total thrips population in SHB varieties. 2012. The number of thrips sampled from the flowers (Fig. 3 10) was significantly different between Feb 23rd and the previous sampling dates ( F = 11.40; df = 2, 2 4; P = 0.0003). There was no effect of block ( F = 1.15; df = 2, 6; P = 0.40) on observed thrips numbers or a varietal effect ( F = 0.84; df = 2, 6; P = 0.48). Sticky trap samples (Fig.3 11) showed that there was no difference in thrips numbers among the sam ple dates ( F = 1.95; df = 3, 32; P = 0.14). There was also no block effect ( F = 1.45; df = 2, 6; P = 0.34) or varietal effect ( F = 0.73; df = 2, 6; P = 0.54) on observed thrips numbers.
39 Total thrips population in SHB varieties. 2013. In year 2 of the study there were significant differences in the number of thrips collected from the flowers ( F = 24.58; df = 4; P < 0.0001) of the 3 treatments over the study period (Fig.3 12). Samples collected on January 28 th 31 st and Feb 11 th were different from those coll ected on both February 4 th and 7 th ( F = 11.44; df = 4, 40; P < 0.0001). Varietal effects were not observed ( F = 0.72; df = 2, 4; P = 0.54) and no block effects were seen ( F = 1.57; df = 2, 4; P = 0.31). Sticky trap counts (Fig. 3 13) showed a significant d ifference in the number of thrips captured ( F = 16.49; df = 4, 16; P < 0.0001) between the sampling dates. There was no block effect ( F = 4.96; df = 2, 4; P = 0.0826) and not varietal effects detected ( F = 3.84; df= 2, 4; P = 0.1174). Total thrips populat ion in Rabbiteye varieties. 2012. Total thrips numbers from flower samples (Fig. 3 14) were significantly different on March 27 th and 30 th from the other 6 sampling dates ( F = 10.07; df = 7, 88; P < 0.0001). Block effects were not detected ( F = 1.15; df = 3, 6; P = 0.40) and no varietal effects were detected ( F = 0.84; df = 2, 6; P = 0.48). Sticky trap counts (Fig. 3 15) show that there is a significant difference in the total number of thrips captured weekly ( F = 18.60; df = 2, 12; P = 0.0002) over the sam pling period. No block effect ( F = 0.78; df = 3, 6; P = 0.54) but varietal effects ( F = 2.88; df = 2; P = 0.1331) were detected. Total thrips population in Rabbiteye varieties. 2013. Flower counts in the second year of data collection showed where thrips numbers were higher in the variety Powderblue than Brightwell earlier in the season but as the season progressed this difference was no longer evident.
40 Sticky trap data show no difference in the thrips population until the fourth week of sampling where th e numbers recorded in the variety Powderblue was significantly higher than in Brightwell but was similar to the numbers recorded in the mixed plot of both varieties. Discussion Mixed cropping does not seem to reduce thrips populations in blueberries when compared with pure stands. Our findings indicate that at the beginning of the season the number of thrips in small plots with a single variety was similar to those with mixed varieties. However, as the season progressed, some differences between single va rietal plots and mixed plots began to appear in SHB where the variety Emerald tended to have more adult thrips than Jewel [Fig. 3 2]. The number of thrips in the mixed plots were often the same or lower than Jewel but this was not consistent throughout the sampling period. This finding is supported by previous work by Rhodes et al. (2012) popula tion dynamics of F. bispinosa does not change between the SHB varieties when investigated in small blocks. This is an important finding since many growers plant SHB varieties either as alternating strips of two or more varieties or in small blocks of a sin gle variety. The results from the mixed plots in rabbiteye blueberries were similar to that in SHB and showed no clear trend throughout the season. Rabbiteye blueberries bloom approximately a month later than SHB, by this time thrips populations on wild h osts and SHB has built up and thrips will migrate in large numbers into a rabbiteye planting.
41 Flower thrips populations may be influenced by blueberry varieties that flower at different times which depend on the number of chill hours required to initiate flowering. The Rabbiteye variety Powderblue flowers before Brightwell while the SHB variety Emerald flowers more uniformly than Jewel (Rhodes et al. 2012). Therefore, some varieties may serve as inoculum for later flowering varieties in the same field and thus diminishing the differences in pest populations between plots and could account for the mixed plots having comparable pest pressure as the pure stands. These results are in contrast to those found by Matteson (1982) who saw a 42% reduction in Megaluro thrips sjostedti (Trybom) numbers when a mixed cropping system of cowpea with maize was used Several studies have shown that insect populations are reduced in mixed cropping systems and crops interplanted with nonhost cover crops (Manandhar et al. 2009). These studies support the idea that nonhost crops planted within the same field as the cash crop can serve as habitats for conserving and increasing populations of natural enemies, therefore introducing diversity into agroecosystems for improved pest contr ol (Platt et al. 1999). Vegetational diversity within an agroecosystem can either be accomplished by intercropping two crops within one agricultural field, or planting several varieties of a particular crop (Liburd et al. 2008) which are usually geneticall y unrelated crops. However, if the varieties grown in a mixed cropping system are genotypically similar, the diversity required to make mixed cropping a viable control tool for pest management would be absent from the system and in that case mixed cropping may not serve to reduce pest populations.
42 Monitoring techniques can be identical simplifying IPM practices for the growers and action thresholds could be the same negating the need to adjust data based on the different varieties that may be grown. The cu rrent study also consistently showed that both in rabbiteye blueberries and SHB that using mixed plots as opposed to plots of single variety does not reduce the incidence of F bispinosa Figure 3 1. Mean number of adult thrips per flower sample record ed from each treatment per week on commercial farm in Citrus Co. in 2012. Error bars represent standard error of the mean 0 50 100 150 200 10-Feb 11-Feb 12-Feb 13-Feb 14-Feb 15-Feb 16-Feb 17-Feb 18-Feb 19-Feb 20-Feb 21-Feb 22-Feb 23-Feb Mean number of thrips Date Jewel Jewel+Emerald Emerald
43 Figure 3 2. Mean number of thrips per flowers sample recorded from each treatment per week and separated into adult and larval li fe stages. Data recorded from a commercial farm in Citrus Co. in 2012. Error bars represent the standard error of the mean Figure 3 3. Mean number of thrips per sticky trap recorded from each treatment per week on commercial farm in 2012. Error bars re present standard error of the mean 0 20 40 60 80 100 120 140 160 180 Adults Larvae Adults Larvae Adults Larvae Week 1 Week 2 Week 3 Mean number of thrips Time Jewel+ Emerald Jewel Emerald 0 2000 4000 6000 8000 Mean number of thrips Date Jewel Jewel+Emerald Emerald
44 Figure 3 4. Average number of adult thrips per flower sample recorded from each treatment twice weekly on a commercial farm in 2013. Error bars represent standard error of the mean Figure 3 5. Mean number of thr ips per flowers sample recorded from each treatment per week and separated into adult and larval life stages. Data recorded from a commercial farm in Citrus Co. in 2013. Error bars represent the standard error of the mean 0 20 40 60 80 100 120 140 Mean number of thrips Date Jewel Jewel+Emerald Emerald 0 20 40 60 80 100 120 Adults Larvae Adults Larvae Adults Larvae Week 1 Week 2 Week 3 Mean number of thrips Time Jewel+ Emerald Jewel Emerald
45 Figure 3 6. Mean number of larv al thrips per flower sample recorded from each treatment twice weekly on a commercial farm in 2013. Error bars represent standard error of the mean Figure 3 7. Mean number of adults thrips per flower sample recorded from each treatment collected twice weekly at PSREU in 2012. Error bars represent standard error of the mean 0 20 40 60 80 100 120 140 160 180 Mean number of thrips Dat e J J+E E 0 50 100 150 200 250 Mean number of thrips Date Powderblue Brightwell Powderblue+Brightwell
46 Figure 3 8. Average number of adults thrips per flower sample recorded from each treatment collected twice weekly in rabbiteye blueberries at PSREU in 2013. Error bars represent standard error of the mean Figure 3 9. Total number of adults thrips per sticky trap recorded from each treatment collected once weekly in rabbiteye blueberries at PSREU in 2013. Error bars represent standard error of the mean 0 100 200 300 400 500 600 12-Mar 14-Mar 16-Mar 18-Mar 20-Mar 22-Mar 24-Mar 26-Mar 28-Mar 30-Mar 1-Apr 3-Apr 5-Apr 7-Apr 9-Apr 11-Apr 13-Apr 15-Apr 17-Apr 19-Apr Mean number of thrips Date Powderblue Brightwell Powderblue+Brightwell 0 500 1000 1500 2000 2500 3000 Mean number of thrips Date Powderblue Brightwell Powderblue+Brightwell
47 Figure 3 10. Total num ber of thrips sampled from flower buds in each treatment collected once per week at a commercial farm in Citrus Co. Florida in 2012. Error bars represent standard error of the mean Figure 3 11. Total number of thrips caught on sticky traps in each tre atment, collected once per week at a commercial farm in Citrus Co. Florida in 2012. Error bars represent standard error of the mean 0 50 100 150 200 250 300 10-Feb 11-Feb 12-Feb 13-Feb 14-Feb 15-Feb 16-Feb 17-Feb 18-Feb 19-Feb 20-Feb 21-Feb 22-Feb 23-Feb Mean number of thrips Date Jewel Jew+Emer Emerald 0 2000 4000 6000 8000 10-Feb 12-Feb 14-Feb 16-Feb 18-Feb 20-Feb 22-Feb 24-Feb 26-Feb 28-Feb 1-Mar 3-Mar Mean number of thrips Date Jewel Jew+Emer Emerald
48 Figure 3 12. Total number of thrips sampled from flower buds in each treatment collected twice per week at a commercial farm in Citrus Co. Florida in 2013. Error bars represent standard error of the mean Figure 3 13. Total number of thrips caught on sticky traps in each treatment, collected once per week at a commercial farm in Citrus Co. Florida in 2013. Error bars rep resent standard error of the mean 0 50 100 150 200 250 28-Jan 29-Jan 30-Jan 31-Jan 1-Feb 2-Feb 3-Feb 4-Feb 5-Feb 6-Feb 7-Feb 8-Feb 9-Feb 10-Feb 11-Feb Mean thrips numbers Date Jewel Jew+Emer Emerald 0 100 200 300 400 500 600 31-Jan 1-Feb 2-Feb 3-Feb 4-Feb 5-Feb 6-Feb 7-Feb 8-Feb 9-Feb 10-Feb 11-Feb 12-Feb 13-Feb 14-Feb Mean number of thrips Date Jewel Jew+Emer Emerald
49 Figure 3 14. Total number of thrips per flower sample recorded from each treatment collected twice weekly at PSREU in 2012. Error bars represent standard error of the mean Figure 3 15. Total number of thrips caught on sticky traps in each treatment, collected once per week at PSREU in 2012. Error bars represent standard error of the mean 0 50 100 150 200 250 27-Mar 29-Mar 31-Mar 2-Apr 4-Apr 6-Apr 8-Apr 10-Apr 12-Apr 14-Apr 16-Apr 18-Apr 20-Apr Mean number of thrips Date Powderblue Brightwell Powderblue+ Brightwell 0 200 400 600 800 1000 1200 1400 6-Apr 7-Apr 8-Apr 9-Apr 10-Apr 11-Apr 12-Apr 13-Apr 14-Apr 15-Apr 16-Apr 17-Apr 18-Apr 19-Apr 20-Apr Mean number of thrips Date Powderblue Brightwell Powderblue+ Brightwell
50 Figure 3 16. Total number of thrips per flower sample recorded from each treatment collected twice per week at PSREU in 2013. Error bars represent standard error of the mean Figure 3 17. Total number of thrips recorded per treatment on sticky traps collected once weekly in rabbiteye blueberries at PSREU in 2013. Error bars represent standard error of the mean. 0 100 200 300 400 500 600 700 12-Mar 14-Mar 16-Mar 18-Mar 20-Mar 22-Mar 24-Mar 26-Mar 28-Mar 30-Mar 1-Apr 3-Apr 5-Apr 7-Apr 9-Apr 11-Apr 13-Apr 15-Apr 17-Apr 19-Apr Total number of thrips Date Powderblue Brightwell Powderblue+ Brightwell 0 1000 2000 3000 4000 5000 6000 7000 15-Mar 22-Mar 29-Mar 5-Apr Total number of thrips Dates Powderblue Brightwell Powderblue+Brightwell
51 CHAPTER 4 EF FECT OF HUMIDITY ON THE REPRODUCTIVE CAPACITY OF FRANKLINIELLA BISPINOSA AND FRANKLINIELLA OCCIDENTALIS (THYSANOPTERA: THRIPIDAE) The western flower thrips Frankliniella occidentalis (Pergande) is among the idespread occurrence and its efficient ability to spread tomato spotted wilt virus (TSWV). Frankliniella occidentalis is native to western North America including the countries of U.S.A, Canada and Mexico. Its extensive spread worldwide can be attributed p rimarily to the movement of agricultural products such as cuttings, seeds, and whole plants. It was commonly referred to as a greenhouse pest but has since become established outdoors especially in areas with milder winters; it is now established across th e entire U.S.A., Australia and southern Europe (Kirk & Terry 2003). There are many other economically important thrips pest species in the genus Frankliniella ; in Florida, the Florida flower thrips, Frankliniella bispinosa (Morgan) is common. This species predominates in the peninsular region of Florida and can be found year round on a wide range of cultivated and uncultivated plants (Reitz 2002, Childers and Nakahara 2006, Rhodes and Liburd 2011). It is a known pest of blueberries and citrus where it inju res floral parts leading to damage of the resulting fruits (Childers 1999, Childers 1991, Arvalo 2006). A related species, the eastern flower thrips, Frankliniella tritici (Fitch), is commonly found in the eastern part of the United States but has been replaced by F. bispinosa in the peninsula of Florida, suggesting that it was being excluded by F. bispinosa. Frankliniella tritici is still not common in the peninsula of Florida when compared to F. bispinosa (Kirk 2002). Frankliniella occidentalis can be found in Florida but is predominantly in the panhandle region of the state (Chellemi 1994); the north
52 central and central regions are predominantly F. bispinosa with the other species occurring in low numbers (Arvalo 2006; Hansen et al. 2003, Childers 199 2, Childers et al. 1999, Rhodes and Liburd 2011). Regions where F. bispinosa dominates the other two species are restricted and vice versa (Reitz 2002, Kirk 2002, Arvalo 2006, Paini 2008). The invasive F. occidentalis is four times as competitive as the n ative species, F. bispinosa and is not affected by interspecific competition from F. bispinosa (Northfield 2005). Frankliniella occidentalis is a known vector of tomato spotted wilt virus (TSWV) and is a threat to the solanaceous industry in Florida (Eckel et al. 1996, Salguero et al. 1991). Similarly, F. bispinosa has also been shown to transmit TSWV in peppers under experimental conditions though at very low rates when compared to F. occidentalis (Avila et al. 2006). The distribution of thrips populations can be influenced by a number of factors including temperature and humidity. Arvalo and Liburd (2007) recorded a clumped distribution of F. bispinosa in blueberry plantings in Florida which they described as hot spots. The formation of these hot spots wa s presumed to be random and that factors such as temperature and humidity were believed to play a role in the development of hot spots. In 1948 Andrewartha et al. published work from a 14 year study that was conducted on Thrips imaginis (a flower thrips) at the Waite Research Institute in Australia. They concluded that temperature had the strongest influence on the population dynamics of this species and humidity was also an important factor (Davidson and Andrewartha 1948 a 1948 b ).
53 Therefore, we hypothesi zed that F. bispinosa would require a higher relative humidity to reproduce than F. occidentalis The primary goal of this paper was to compare these two flower thrips species commonly found in Florida to determine if relative humidity influences the distr ibution pattern that currently is observed. They are both economically important pests in Florida affecting different crops; however, there is no significant overlap in their geographical ranges. Materials and Methods Colony Establishment Frankliniella b ispinosa were collected from southern highbush blueberry (SHB) flowers from commercial farms in Citrus Co. Florida. Thrips were removed from flowers using a vacuum extraction pump (IN26 Air compressor and vacuum, GAST Manufacturing INC., MI) modified for s mall insects including thrips. A sample was slide mounted and examined under the light microscope to confirm that the species was F. bispinosa using the thrips identification key developed by Arevalo et al. (2009 b ). Pesticide free, organic green beans ( Ph aseolus vulgaris ) were provided as a food source. Beans were initially soaked in 3.5% Fit Fruit and Vegetable Wash (HealthPro Brands Inc, Cincinnati, OH) solution to remove any pesticide residues that may be present, then thoroughly rinsed in deionized tap water and air dried before being put into the colony. Thrips were placed in Ziploc entre containers (22 cm 14 cm) (SC Johnson and Son, INC, WI) in an environmental growth chamber (Percival I 36, Percival Scientific INC, IA) at 23 1 C, 85 10% RH an d photoperiod of 14 L: 10 D. Green beans were placed on filter paper (Fisherbrand Filter paper, Grade: P8, 15cm diameter; Pittsburg, PA) inside containers. Separate weigh boats of honey and
54 grounded bee pollen were included in each container to promote rep roduction. Containers containing thrips were serviced 2 times per week, on Mondays and Fridays. During the service operation, old or diseased green beans were replaced by fresh ones and new filter papers replaced old ones; fresh honey and bee pollen was pr ovided as needed. Frankliniella occidentalis was obtained from an established colony (USDA Tallahassee laboratory, Florida) was reared in the same manner as F. bispinosa but with a lower humidity, at 23 1 C, 6510% RH. Humidity Experiments Washed gr een beans was cut into 2 cm lengths, each end was sealed with melted paraffin wax and allowed to cool. A single piece of bean (2 cm long) was placed into each of 10 SOLO P100 cups (SOLO cup Company, Lake Forest, IL). Two F. bispinosa adults were placed in each of the ten SOLO P100 cups which was covered with lids that had their centers replaced with 0.1 mm mesh screen; these procedures were repeated using F. occidentalis. The cups were then placed into an Environmental chamber at 23 1 C, 12:14 L: D photo period with a RH of 40%; this set up was replicated at 55%, 70% and 80% RH. Thrips adults were left to oviposit on the beans and adults were removed from the cups after a period of 24 hours using the vacuum suction pump (described above) the cups with only eggs were then returned to their respective environmental chamber. The number of larval thrips in each container was recorded at 12 hour intervals for at least 6 days. The reproductive capacity and time to emergence was recorded for each species at each s ampling period. Data was analyzed
55 paired t tests. Results Varying the humidity at a set temperature had a significant effect on the reproductive capacity of both flower thrip s species. The mean reproductive capacity was higher at 70% RH than at 40% at all sampling times for both thrips species. The reproductive capacity of F. bispinosa was significantly higher at 70% relative humidity than the other humidities studies at time 60, 72, 84 and 96 hours after completion of the ovipositional period. After 5 d (108 hours), there were significant differences in the reproductive capacity of F. bispinosa at the humidities studied ( F = 5.46; df = 3; P = 0.0034). The reproductive capacity at 70% RH of F. bispinosa was comparable to that at 80% at 108 hrs, however, it was statistically higher than the rates observed at both 55% and 40% relative humidity (F = 5.46; df = 3; P = 0.003) for the same species. After 120 hours, the reproductive ca pacity was higher in 70% and 50% RH treatments when compared to the 80% and 40% RH treatments. The reproductive capacity of F. occidentalis at the various humidities was comparable for the 1 st 60 hours after oviposition and hardly any reproduction took pla ce. However, at 72 hours there were significant differences with the reproductive capacity observed, being higher at 70% RH than at 40% and 55% RH ( F = 3.84; df = 3; P = 0.017). At 84 hours post oviposition, the reproductive capacity observed at 70%RH was significantly higher than 40% ( F = 3.93; df = 3; P = 0.016) however, this rate was similar to the rates observed at 55% and 80% RH. The reproductive capacity of F. occidentalis
56 at 96, 108 and 120 hours post oviposition [Fig. 4 2] was significantly higher a t 55% RH than at 40%RH but not higher than those rates observed at 80% and 70% RH Frankliniella bispinosa larvae hatches earlier at higher humidities of 70% and 80% at least 2 days earlier than at lower humidities of 55% and 40%( F =37.38; df = 3; P = <0.000 1) [Fig. 4 1]. Frankliniella occidentalis larvae took significantly longer than F. bispinosa larvae to emerge at relative humidities of 80% ( t = 4.33; df =16.21; P = 0.0004) [Fig. 4 3] and at 70% ( t = 4.63; df = 17.73; P = 0.0002). At a relative humidity of 55%, F. occidentalis emerged significantly earlier than F. bispinosa ( t = 4.31; df = 17.98; P = 0.0004) with a mean emergence time of 88.8 hours when compared to 108 hours taken by F. bispinosa At 40% relative humidity, F. occidentalis took longer to emerge as larvae than F. bispinosa (t = 2.52; df = 13.54; P = 0.024) with a mean time of emergence of 151.2 hours and 109.2 hours, respectively. Emergence time was longer for F. occidentalis at 40% RH than at any of the other relative humidities studied ( F = 14.37; df = 3; P = <0.0001). Discussion The reproductive potential of both F. bispinosa and F. occidentalis can be influenced by changes in humidity as shown in this current study. The reproductive capacity of F. bispinosa tended to be higher than tha t of F. occidentalis at most all of the humidity regimes studied, this does not completely support the findings of previous literature that recorded higher reproductive rates for F. occidentalis (Lublinkhof and Foster 1977). The studies of Lublinkhof and F oster (1977) did not include species in this current study and looked at the net reproductive rate based on one generation; this study only compared the potential of the two species to reproduce in response to
57 different humidity regimes and did not account for mortality or the rate of survival through the various life stages as this had been extensively studied in previous research (Bi song 2001). As discussed in Hulshof and Vanninen (2002) and Tsai (1996), diet plays a great role in the fecundity of both F occidentalis and F. bispinosa ; the addition of pollen can increase reproduction. In the current study, thrips species had no source of pollen during the ovipositional period as it was the aim to determine the reproductive potential in the absence of food sources or in the presence of low quality food sources such as beans to establish a minimum reproductive capacity. Green beans ( Phaseolus vulgaris ) has always been used as a substrate for the laboratory rearing of F. occidentalis, however, reproductive ca pacity on beans may not be as high as on other substrates studied such as cucumber leaves (Hulshof and Vanninen 2002). Temperature is known to have an effect on the fecundity of F. occidentalis where optimum egg hatch occurs around 20C with a life cycle of about 22 days primarily due to the reduction in development time in the egg and larval stages (Lublinkhof and Foster 1977). Based on the current study, it has been shown that at constant temperatures, humidities above 70% and below 55%RH result in a lon ger emergence period; this would increase the total development time and result in fewer generations per year thus influencing the pest status of F. occidentalis In a survey carried out by Chellemi (1994) in north Florida on wild uncultivated plants, F. o ccidentalis was most abundant in the months February to July while F. bispinosa was present between March and August; earlier infestation gave a competitive edge to F. occidentalis but as the summer progressed and became more humid, F. bispinosa became abu ndant. These findings can be explained by the current study where F. bispinosa had a higher reproductive
58 capacity at higher relative humidities and emerged earlier, leading to a faster generation time than F. occidentalis which takes a significantly longer time to emerge as larvae at humidities higher than 70% The findings of the current study showed that F. bispinosa requires higher humidity than F. occidentalis to reproduce; it reproduces poorly at humidities below 70% RH. Conversely, F. occidentalis ca n reproduce at high humidities but reproduces better at mid range humidities of 55% and 70%. Neither species reproduced well at low humidities, this can be explained by their flower inhabiting nature and large surface to volume ratio that can promote desic cation in small insects. This study did not compare survival rates or mortality at the various larval stages; however, in the future it may be necessary to investigate the effect of humidity on these factors to determine the magnitude of influence it may e xert on populations of these two species. The variation in geographic distribution of F. bispinosa and F. occidentalis cannot be explained solely on the influence of humidity on their reproductive potential; a number of interacting factors may be responsib le for the phenomenon observed in north Florida such as predation, temperature, reproductive host availability, inter specific and intra specific competition.
59 Figure 4 1. Mean reproductive capacity of F. bispinosa incubated at 23C and four different Re lative humidities (80%, 70%, 55% and 40%). Error bars represent the standard error of the mean Figure 4 2. Mean reproductive capacity of F. occidentalis incubated at 23C and four different Relative humidities (80%, 70%, 55% and 40%). Error bars repres ent the standard error of the mean 0 2 4 6 8 10 12 24 36 48 60 72 84 96 108 120 132 144 Mean reproductive capacity Time (hours) 80% 70% 55% 40% 0 1 2 3 4 5 6 24 36 48 60 72 84 96 108 120 132 144 Mean Reproductive capacity Time (hours) 80% 70% 55% 40%
60 Figure 4 3. Mean time taken for F. bispinosa (FFT) and F. occidentalis (WFT) larvae to emerge following ovipositional period of adults at 23C and varying relative humidities (40%, 55%, 70% and 80%). Error bars repres ent the standard error of the mean. 0 20 40 60 80 100 120 140 160 180 40 55 70 80 Mean time to emergence (hrs) Relative humidity (%) FFT WFT
61 CHAPTER 5 DE VELEOPMENT OF A RISK BASED PREDICTIVE MODEL FOR FRANKLINIELLA BISPINOSA IN SOUTHERN HIGHBUSH BLUEBERRIES GROWN IN FLORIDA Frankliniella bispinosa Morgan is a major early season pest in blueberry product ion in Florida in the US (Arevalo 2006). This species predominates in the peninsular region of the state and coincides with the southern highbush blueberry growing areas. Frankliniella bispinosa is an insect and belong to the order Thysanoptera (thrips); t hey are minute insects with characteristic rasping sucking mouthparts, which often determine the type of injury they cause to host crops. The abundance of this pest in the blueberry cropping system varies from year to year and may be more devastating in so me years more than others. The use of models to forecast diseases or to predict pest occurrence is a relatively new trend in agriculture that seeks to remove much of the guesswork that had previously been involved in crop protection. Research in integrated pest management (IPM) has led to a bank of knowledge, which now requires computer aided methods for their integration, interpretation and delivery (Coulson 1992) to move the agricultural industry forward. Currently, in Florida there is an advisory system in strawberries Strawberry Advisory System (SAS) that forecasts the risks of pathogens. The use of this tool has reduced the number of fungicide sprays by about 50% (MacKenzie and Peres 2012) subsequently reducing production costs. The model measures leaf wetness and temperature, which are used to predict disease outbreak. This web based predictive model uses data from the Florida Agricultural Weather Network (FAWN), which has numerous weather stations across the state of Florida. With internet access, gro wers are able to predict disease incidence along with fungicide recommendations. Alerts can
62 also be sent to growers via email and text messages (Pavan et al. 2011). There is no such system for predicting risks to crops by insect pests in Florida. The predi ction of pest development and emergence based on weather models will be a very useful tool in enhancing IPM of F. bispinosa in blueberries in Florida. Research has been carried out in more temperate parts of the United States on developing an effective to ol for predicting the abundance of thrips in blueberry cropping systems. However, based on the literature this model was created using a statistical approach where a regression model was fitted to available data. The use of this tool cannot be extended to other areas because of the inadequacies associated with the method in which it was derived. Nevertheless, this model using regression analysis has since been proven effective in New Jersey where it was developed and has been incorporated into the forecasti ng system for Frankliniella tritici Fitch emergence and abundance in New Jersey (Rodriquez et al. 2010). In 1948 Andrewartha et al. published work from a 14 year study that was conducted on the flower inhabiting Thrips imaginis Bagnall (Australian plague t hrips) at the Waite Research Institute in Australia. They concluded that this species exhibited a logistic rate of growth but at different rates over the course of the year (Davidson and Andrewartha 1948 a ); they also concluded that of all the environmental factors studied temperature had the strongest influence on the population dynamics of this species. This is the most extensive work to date carried out on a flower inhabiting thrips species. Frankliniella bispinosa is the Florida flower thrips and is foun d in the north central region to south of the state. It has numerous alternate hosts which it inhabits (Rhodes and Liburd 2011) and can be a significant pest in blueberry plantings during the flowering
6 3 period between February and April. This pest is season al and is not damaging every year, however, when there is an infestation yields can be significantly affected. The development of thrips is highly influenced by environmental factors including temperature (Davidson and Andrewartha 1948 b ); therefore, monito ring degree days or daily average temperatures can be helpful in predicting their abundance in blueberry plantings so that management actions can be taken. In New Jersey where the eastern flower thrips ( F. tritici Fitch) is common, a degree day model to pr edict their abundance has been developed; with a base temperature of 50 F, 10%, 50% and 90% of thrips captures had been observed at 380, 650 and 1200 degree day accumulation, respectively (Pavlis 2010). In another study, Olatinwo et al. (2008) tested the Weather Research and Forecasting (WRF) model and its reliability in predicting the occurrence of vectors of Tomato spotted wilt virus (TSWV). They were able to produce high resolution reliable maps for favorable conditions and scouting guidelines even in a reas where weather data was limited. The development of a predictive model that is user friendly and available to blueberry growers would be very useful as a decision making tool to aid in the management of the Florida flower thrips. We hypothesized that the abundance of F. bispinosa in Florida can be predicted using a temperature based model. Therefore, the specific objective of this study is to 1) develop a dynamic model based on temperature to predict the abundance of the thrips F. bispinosa in blueberr y crops in north central Florida.
64 Materials and Methods Model Development Davidson and Andrewartha in 1948 produced a number of graphs to describe the thrips populations observed over the course of their 14 year study. A logistic curve summarizing the me an population for 7years was reproduced through approximation using digitization techniques. This data set coincided with the period of winter to spring months in Australia and was also the time when thrips populations were recorded at their highest. In th e absence of temperature data for the period in which the study was conducted, a 20 year (from 1992 2012) daily average was calculated for the Waite Research Institute (retrieved from NASA website for study site) and was used for subsequent analysis. The simulated population based on the model created is plotted on top of the actual p opulation is shown in Fig 5 2 Where the observed population is shown in black and the simulated population is shown in red. Parameter estimation was carried out using the Opt im function in R. The initial parameter values were estimated using this equation developed by Andrewartha et al: where Y represented the average number of thrips per flower on a given date x d is the height of the lower asymptote, K is the height of th e upper asymptote and a and b are constants calculated from the data. The initial values supplied to Optim of Yo was 1, Ymax was 647 and M was 0.38. The software R through a series of iterations estimated best values for each parameter. A sensitivity analy sis was also carried out using
65 Data Collection Thrips population data were collected for 2 years from a planting of Southern highbush blueberry (SHB) on a commercial fa rm in Marion Co. FL. Blueberry plants were ~ 5 years old and 1.2 m in height. Planting pattern consisted of four rows each of a single variety. This pattern was consistent throughout the entire farm with the series of varieties being: Star, Emerald, Millen ia and Windsor. Each block consisted of four rows and was replicated 3 times; data were collected once per week for both years of study. Data were averaged according to treatment for each week and used in testing the model. Results A Forrester diagram was created to describe the components of the system (Fig.5 1) and described in Table 5 1. Based on the observation of Davidson and Andrewartha (1948 a ) that the population exhibited a logistic pattern, the typical logistic equation was incorporated into the d ynamic model. The model was defined by: Y[t+1] = Y[t]+dY Where: dY = M*Y[t]*(1 (Y/Ymax)) M is the population growth rate Y is the popupaltion on any given day [t] Ymax is the maximum or asymptote of the population
66 Parameter Estimation Parameters were est imated using the Optim function in R. The parameter Yo was estimated at 12.32, Ymax at 633.46 and M at 0.357. There was convergence and the sum of squares was rather high at 191909.2. Validation The model was tested in Florida without being calibrated u sing weather data from the FAWN station in Citra, Marion Co (Fig. 5 3 & 5 4). Discussion There are some basic assumptions that were made in order to create this model. The first assumption that temperature is the only driving factor in this system can cle arly be seen to not be true. This can be observed in the difference between the observed and predicted population size both in the simulation of the population of T. imaginis and F. bispinosa Davidson and Andrewartha (1948 b ) had carried out a series of re gression analyses and determined that temperature was the most important environmental factor that influences the population of T. imaginis however, temperature was not the only factor that explained the dynamics observed within that thrips populations. The temperatures used to create the model were not the actual temperatures in 1948 at the Waite Research Institute; however, in the absence of that dataset a 20 year average was used. This was with the assumption that the temperature for that location had not changed much in the last 80 years. Also, by using a 20 year average, it is assumed that any anomalous data will be evened out and thus using this would be a
67 good estimate of the temperature within this region during the time the study took place. This assumption could have resulted in an increase in errors in the model. the number of thrips found in its samples collected in 2012 and 2013 growing season was not determined to be different from 3 of the more commonly planted SHB varieties: Emerald, Windsor and Millenia (unpublished data). This model is based solely on the influence of temperature; however there are other factors including relative humidity, crop phenology, and alternative host that influence thrips populations in a blueberry planting; therefore, the model was unable to predict F. bispinosa in the field using flower samples or trap catches. Frankliniella bispinosa are only observed in the field during the bloomin g period; hence the inclusion of such a condition in the model would be relevant. It has also been recently shown that thrips development and reproduction can be influenced by low humidities; this should also be included in refining this model. More resea rch is needed to explore how crop phenology and humidity in conjunction with temperature influences populations of thrips in blueberry plantings. These parameters will need to be included in subsequent improvements of the model since the simple model was i nsufficient to accurately model the system.
68 Figure 5 1. Relational diagram describing the components of the system for Frankliniella bispinosa in SHB blueberries in Florida
69 Figure 5 2. Simulated population of T. imaginis overlaid on a plot of the av erage population observed for a 7 year period 1932 7 at the Waite Research Institute Figure 5 3. Simulated values using temperature data from Florida 2012 compared to recorded abundance of thrips in flower and sticky trap samples collected from the vari ety Star at a farm in Marion Co. Florida 0 50 100 150 200 250 300 350 27-Jan-12 1-Feb-12 6-Feb-12 11-Feb-12 16-Feb-12 21-Feb-12 26-Feb-12 2-Mar-12 7-Mar-12 Thrips population Date Simulated Flowers Traps
70 Figure 5 4. Simulated values using temperature data from Florida 2013 compared to recorded abundance of thrips in flower and sticky trap samples collected from the variety Star at a farm in Marion Co. Florida Table 5 1. Description of Forrester diagram of system of Frankliniella bispinosa in a blueberry planting Variables Description and dimensions State variables Eggs Proportion of eggs in the population at time t 1 st instar Proportion of 1 st larval ins tar in the population at time t 2 nd instar Proportion of 2 nd larval instar in the population at time t Propupa Proportion of propupa in the population at time t Pupa Proportion of pupa in the population at time t Adult Proportion of adults in the popul ation at time t Rate variables 0 20 40 60 80 100 120 140 160 180 27-Dec-12 6-Jan-13 16-Jan-13 26-Jan-13 5-Feb-13 15-Feb-13 25-Feb-13 Thrips population Date Simulated Flowers Traps
71 Table 5 1. Continued Variables Description and dimensions D1 Rate of development egg from time laid to hatched (per unit t) D2 Development rate of 1 st larval instar to molt into 2 nd instar (per unit t) D3 Developmen t rate 2 nd larval instar to molt to propupa (per unit t) D4 Developmental rate of pupa into adult (per unit t) M1 Mortality rate of eggs (per unit insect) M2 Mortality rate of 1 st larval instar (per unit insect) M3 Mortality rate of 2nd larval instar ( per unit insect) M4 Mortality rate of propupa (per unit insect) M5 Mortality rate of pupa (per unit insect) M6 Mortality rate of Adult(per unit insect) R Rate of reproduction or replacement of progeny from adult population (per unit insect) Dispersal rate The rate at which thrips migrate from flower buds Auxiliary variables Crop phenology Crop stage influences abundance; no/low numbers of flowers influences migration Thrips Density Carrying capacity influences rate of dispersal
72 CHAPTER 6 LABORAT ORY REARING PROTOCOL FOR ESTABLISHMENT AND MAINTENANCE OF A COLONY FOR F RANKLINIELLA BISPINOSA (MORGAN ) Frankliniella bispinosa (Morgan) is commonly referred to as the Florida flower thrips (FFT) and is the dominant species in the peninsula of Florida pri marily in the central to north central regions. It is a key pest in early season blueberry plantings in central and north central Florida. Injury caused by the rasping sucking mouthparts to floral parts results in damage to the subsequent berries produced. Flower drop associated with infestation of F. bispinosa and scarring damage on fruits leads to a reduction in yield for growers (Arevalo et al. 2009, England et al. 2007). Adult and larval thrips feed on floral tissues including pollen, pistils, petals and associated nectar. Nectar is a carbohydrate rich substance with small amounts of proteins, amino acids, lipids, vitamins, secondary plant compounds, organics compounds and minerals; pollen has a high nitrogen content in addition to sterols, lipids and starch (Wackers et al. 2007, Ball 2007). The nectar in the Vacciniaceae (blueberry plant group) is predominantly composed of fructose and glucose with sugar content ranging from 36 57% (Percival 1961, Jablonski et al. 1985). Some studies have shown that ad ding pollen greatly enhances reproduction capacity in thrips (Wackers et al. 2007, Tsai et al. 1996). A diet with both nectar and pollen can potentially provide the requisite nutrients for development and reproduction. The rearing of F. bispinosa has been done by a number of researchers in Florida over the years. However, no documented rearing protocol is available and colonies established are usually short term as many struggle to maintain a colony year round; the strict humidity requirements of FFT that w ere not elucidated to date by research is
73 usually the primary reason for colony failure. Since F. bispinosa is such an important pest in Florida blueberry production as well as other vegetable crops it is important to have established guidelines by which a colony of F. bispinosa can be successfully reared in order to study this pest. Therefore the aim of this study was to develop and document rearing guidelines for F. bispinosa from field collected samples in blueberries. Materials and Methods Franklinie lla bispinosa were collected from opened southern highbush blueberry flowers from commercial farms located throughout central Florida. Flowers were placed into Ziploc entre containers (22 cm 14 cm) (SC Johnsn and Son, INC, WI) with a hole in the lid cov ered by thrips mesh to allow for ventilation. Containers were brought back to the Small Fruit and vegetable IPM lab at the University of Florida. A sub sample of 10 adults was collected from the Ziploc containers and slide mounted before being examined un der a light microscope (10 X) to verify that the species was F. bispinosa using the identification keys for thrips in blueberries (Arevalo et al, 2013). Thrips were removed from flowers by using a vacuum pump (IN26 Air compressor and vacuum, GAST Manufactu ring INC. MI) that was attached to a modified aspirator (with a 50 ml centrifuge tube into which a 1.5 ml micro centrifuge tube was attached to the intake tube of the aspirator). Thrips were collected into the micro centrifuge tube while the larger centrif uge tube allowed the maintenance of the vacuum. Pesticide free, organic green beans ( Phaseolus vulgaris ) were provided as a food source. Beans were initially soaked in a 3% solution of Fit Fruit and Vegetable Wash (HealthPro Brands Inc, Cincinnati, OH) fo r 3 minutes to remove any pesticide residues that may be present; beans were then immediately rinsed thoroughly several
74 times in deionized tap water. In the absence of organic beans, conventionally grown beans were used but were triple washed and rinsed. W ashed green beans were then placed on 2 layers of paper towel on the laboratory bench to air dry for at least an hour. Green beans (at least 5) were then placed on filter paper (Fisherbrand Filter paper, Grade: P8, 15cm diameter; Pittsburg, PA) inside rear ing containers. Bee pollen whole granules (Y.S Organic Bee Farms, Sheridan, IL) were grounded to a powder; a weighing dish (41 41 8mm) with approximately 0.5 g of grounded pollen was placed in each rearing container. A 3 cm long piece of cotton wick soak ed in honey (UF IFAS Honey bee Research and Extension lab) diluted to make an 80% solution was placed in another weighing dish and placed inside of the rearing container [Fig. 6 1]. Thrips were placed in rearing containers [Fig. 6 2] (22 cm 14 cm) in an environmental chamber at 23 1 C, 80 10% RH and photoperiod of 16 L: 8 D. Containers containing thrips were serviced twice per week. During the service operation, old or diseased green beans were replaced by fresh ones and new filter papers replaced wi th old ones; bee pollen and honey were replaced as necessary to prevent fungal buildup within the colony and rearing containers were changed as needed. Care was taken to transfer thrips to new green beans without damaging them using a paintbrush. Modificat ions to rearing conditions, by adjusting humidity and the number of beans were made throughout the rearing process for sustaining thrips colony. To get thrips of the same cohort, beans previously placed in the colony at the last servicing operation were r emoved and thoroughly brushed with a paintbrush to remove the adults or larvae present. These beans were then placed in a new rearing container
75 labeled with the date of the current day. First instar larvae will begin to appear 2 3 days later. Results and Discussion The rearing of insect species can become technical as many species may need special conditions to facilitate for colony establishment and maintenance. Based on previous attempts to rear F. bispinosa researchers were aware that F. bispinosa req uired a higher humidity than Frankliniella occidentalis (Pergande) in order to be maintained in a colony; however the specific requirement was unknown. It has now been established from laboratory experiments that F. bispinosa is most fecund at a relative h umidity of 70% when kept at a constant temperature of 23 1C (unpublished data). The improved rearing protocol established for the western flower thrips, F. occidentalis on Persian cucumbers was done at 26 3 C and 37 7% RH (DeGraaf and Wood, 2009), however, at a rearing temperature of 23 1C it was shown in laboratory studies that F. occidentalis was more fecund at relative humidities between 55% and 70%. Fig 6 3 records the relative humidity conditions under which the colony was held. Many research ers in Florida who have recently attempted to rear F. bispinosa have had difficulties maintaining their colony beyond the summer months. The current colony was maintained under the regime described above for 9 months from February to November and is still ongoing. The main advantage with this protocol is that other thrips species can also be reared using these guidelines; with slight adjustments to meet their specific needs. For instance, F. occidentalis requires a lower humidity and by decreasing the humid ity the protocol will work well for this species. The materials used
76 are inexpensive and does not need specialized training to rear F. bispinosa species; this method is also simple and not time consuming. The number of green beans used was important as us ing more than 5 seemed to provide a micro habitat that 1 st instar larvae preferred and were commonly found on the underside of beans in close proximity to each other. Other larval stages were found on all parts of the beans and did not seem to prefer more humid conditions. Both pollen and honey were found to be important in sustaining the colony; when either was omitted a decline in the number of larvae produced in that container was observed soon after. It is also important to always use green beans; yello w beans are usually waxed and somehow seem to reduce oviposition into the beans. No progeny are produced when yellow beans were used as a substrate. This rearing method for F. bispinosa provides a simple yet cost effective, efficient way of maintaining la boratory colonies for research purposes. No specialized laboratory equipment was needed; materials and substrate can usually be purchased at a local grocery and it is neither time consuming nor labor intensive.
77 Figure 6 1. Illustration of layout of rea ring containers for F. bispinosa with the lid removed Figure 6 2. Picture of rearing container (with lid attached) prior to being placed in the environmental chamber
78 Figure 6 3. Average relative humidity of the interior of the environmental chamber for a 7 week period
79 CHAPTER 7 CONCLUSION The results presented in this thesis were related to 4 objectives: 1) to investigate if spatial varietal planting patterns in blueberry fields in Florida influences abundance of F. bispinosa. 2) to investigate th e effects of humidity on the reproductive capacity of two flower thrips species: Frankliniella bispinosa (Morgan) and Frankliniella occidentalis (Pergande). 3) to develop a model to predict the potential risk posed to blueberry crops by F. bispinosa and 4) to develop an improved rearing protocol for F. bispinosa. The field experiment demonstrated that the abundance and dynamics of Frankliniella bispinosa in blueberry fields was similar in both rabbiteye and southern highbush blueberries (SHB). Thrips popula tions in mixed plantings of two varieties were not different from singly planted varieties. Therefore, mixed cropping systems in recommended as a cultural tactic to suppress F. bispinosa populations in blueberry IPM programs until more information becomes available. Further research using different varietal combinations and larger plots is needed to investigate the usefulness of mix ed cropping in blueberries for thrips control in Florida. Environmental factors were long theorized to account for the spatial differences in the geographic range of the native F. bispinosa and the invasive F. occidentalis Laboratory experiments carried o ut at a set temperature and varying humidity demonstrated that the fecundity of both species was affected by changes in humidity. Results confirmed that the native F. bispinosa was more fecund at higher humidities than F. occidentalis The time taken to em erge was also affected by changes in relative
80 humidity as both species took a longer time to emerge at lower humidities. Further research is also needed at different temperatures to determine how temperature changes in combination with changes in relative humidity affects these two species and how that information could lead to further understanding the difference in geographic ranges in Florida. The model was able to simulate the data from which it was created but unable to reliably predict thrips populati ons in blueberry fields in Florida. This can be accounted for by the absence of a humidity factor and a crop phenology factor within the model. These factors are important in thrips development in blueberries in Florida and will need to be included in futu re amendments to the current model. The rearing of F. bispinosa. was determined to proceed best at a temperature of 23 1C and at a relative humidity of 70%10 RH. Under these conditions cohorts of the same age can be obtained. The overall goal of this p roject was to investigate known IPM tools of mixed cropping and forecasting within the blueberry cropping system in Florida. It was also pertinent to look at the effects of humidity on F. bispinosa and compare it with a worldwide invasive thrips species. T he rearing of the Florida flower thrips is essential to facilitate greater research with this pest; a rearing protocol available to researchers can reduce the guesswork and improve efficiency in establishing colonies.
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86 Reitz, Stuart R 2002. Seasonal and within plant distribution of Frankliniella thrips (Thysanoptera: Thripidae) in North Florida tomatoes. Fla. Entomol. 85: 431 439. Rhodes, E. M., and O. E. Liburd. 2011. Flower thrips (Thysanoptera: Thripidae) dispersa l from alternate hosts into southern highbush blueberry (Ericales: Ericaceae) plantings. Fla. Entomol. 94:311 320. Rhodes, E. M., O. E. Liburd, and G. K. England. 2012. Effects of southern highbush cultivar and treatment threshold on flower thrips populat ions. J. Econ. Entomol. 105(2): 480 489. Rodriquez, C. R., S. Polavarapu, J. D. Barry, D. Polk, R. Jornsten, P. V. Oudemans, and O. E. Liburd. 2010. Color preference, seasonality, spatial distribution and species composition of thrips (Thysanoptera : Thri pidae) in northern highbush blueberries. Crop Protection 29:1331 1340. Salguero, V. E., J. E. Funderburk, R. J. Beshear, S. M. Olson, and T. P. Mack. 1991. Seasonal patterns of Frankliniella spp. (Thysanoptera: Thripidae) in tomato flowers. J. Econ. Entomo l. 84:1818 1822. SAS Institute Inc. 2012. The SAS system 9.3 for Windows. SAS Institute, Cary, NC. Steck, G. J., P. M. Lyrene, and J. A. Payne. 2011. Blueberry gall midge, Dasineura oxycoccana (Johnson) (Insecta: Diptera: Cecidomyiidae). University of Flo rida IFAS Extension publication EENY 136, University of Florida, Gainesville, Florida. Theunissen, J., and G. Schelling. 1996. Pest and disease management by intercropping: suppression of thrips and rust in leek. Int. J. Pest Man. 42: 227 234. Triplehorn, C. A., and N. F. Johnson. 2005. study of insects. Thomson Brooks/Cole, Belmont, CA. Tsai, J. H., B. S. Yue, J. E. Funderburk, and S. E. Webb. 1996. Effect of plant pollen on growth and reproduction of Frankliniella bispinosa Acta. Hortic. 431:535 541. Turner, J. C. L., and O. E. Liburd. 2007. Insect management in blueberries in the Eastern United States. University of Florida IFAS Extension publication ENY 411, University of Florida, Gainesville, Florida Wackers, F. L., J. Romeis, and P.van Rijn. 2007 Nectar and pollen feeding by insect herbivores and implications for multitrophic interactions. Annu. Rev. Entomol. 52:301 323. Walsh, D. B., M. P. Bolda, R. A. Goodhue, A. J. Dreves, J. Lee, D. J. Bruck, V. M. Walt Drosophila suzukii (Diptera: Drosophilidae): Invasive Pest of Ripening Soft Fruit Expanding Its Geographic Range and Damage Potential. Journal of Integrated Pest Management, Entomological Society of America. [In press].
87 Weibelzahl, E., and O. E. Liburd. 2010. Blueberry Bud mite, Acalitus vaccinii (Keifer) on southern highbush blueberry in Florida. University of Florida IFAS Extension publication ENY 858, University of Florida, Gainesville, Florida. Williamson, J. 1999. T Association. Gainesville, Florida. Williamson, J. 2000. Association. Summer issue. Gainesville, Florida. Williamson, J. 2001. association. Winter issue. Gainesville, Florida. Williamson, J. 2006. Association. Fall issue. Gainesville, Florida. Willia mson, J. G., and P. M. Lyrene. 2004. Blueberry varieties for Florida. University of Florida IFAS Extension publication HS967, University of Florida, Gainesville, Florida. Williamson, J. G., P. M. Lyrene, and J. W. Olmstead. 2012 a gui de. University of Florida IFAS Extension publication CIR1192, University of Florida, Gainesville, Florida. Williamson, J. G., P. M. Lyrene, and J. W. Olmstead. 2012 b Protecting Blueberries from freezes in Florida. University of Florida IFAS Extension pub lication HS968, University of Florida, Gainesville, Florida. Wright, A. F., and P. F. Harmon. 2009 a First report of Lasiodiploda theobromae associated with stem blight of southern highbush blueberries in Florida. Plant Disease 93: 962 962. Wright, A. F and P. F. Harmon. 2009 b Identification of species in the Botryosphaeriaceae family causing stem blight on southern highbush blueberry in Florida. Plant Disease 94: 966 971. Wright, A. F. and P. F. Harmon. 2009 c Morphological identification and pathoge nicity of Botryosphaeria spp. causing stem blight on southern highbush blueberries in Florida. Phytopathology 99: S143 S143.
88 BIOGRAPHICAL SKETCH perimental biology at the University of the West Indies, Mona, in Kingston Jamaica in 2006. Her undergraduate research looked at investigating the use of bio rationals as alternatives to the use of conventional pesticides in the production of a crop of Ama ranthus viridis a leafy vegetable common to the tropics. In August 2006, she joined the staff at the Edwin Allen High school as a science teacher. She was responsible for preparing senior students of grades 9 13 for the Caribbean regional examinations, a job she held for approximately 3 years. In the summer of 2009 she joined the Doctor of Plant Medicine program (DPM) at the University of Florida. In August 2011, she joined the Small fruit and vegetable IPM laboratory, University of Florida, in Gainesville to pursue her MS in entomology and nematology.
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